Several studies have been published indicating that creatine ingestion greater than 20 g/day for 5 to 7 days increases total muscle creatine concentrations and improves performance during short-duration, high-intensity activities such as resistance training. More recent studies also indicate that creatine supplementation in conjunction with resistance exercise training from 4 to 12 weeks enhances the physiological adaptations to weight training in both men and women. Studies examining the influence of creatine supplementation (5-30 g/day) during weight training (4-12 wks) generally indicate enhanced body mass, including an increase in fat­free mass (FFM), an increase in muscular strength, and the ability to train at higher intensities.

Several lines of research suggest that creatine could playa role in augmenting skeletal muscle fiber hypertrophy. Gyrate atrophy patients who consumed 1.5 g creatine per day for 1 year showed significant increases in type II muscle fiber diameter. Creatine supplementation has also been shown to facilitate muscle rehabilitation following disuse atrophy. In fact, our laboratory recently published data showing that muscle fiber hypertrophy was enhanced in men who consumed 25 g of creatine per day for 7 days followed by a daily 5-gram dose for the remainder of a 12-week resistance training program. In addition, creatine-supplemented subjects showed significantly greater improvements in maximal strength, fat-free mass, and creatine accumulation compared with placebo subjects. The percentage increases in cross­sectional area for all fiber types in creatine subjects ranged from 29-35%, more than twice the increase observed in placebo subjects (6-15%). Greater muscle fiber hypertrophy implies enhanced myofibrillar protein synthesis and/or reduced degradation. Creatine may play a direct role in myosin and actin synthesis in vitro, which may be mediated via cell swelling. A more likely scenario to explain the augmented skeletal muscle fiber cross-sectional areas observed with creatine supplementation is that the intensity of individual resistance training sessions is enhanced (Le., heavier loads can be lihed), leading to a greater stimulus for muscle fiber hypertrophy.

The direct or indirect nature of this anabolic effect of creatine has not been elucidated, however, most researchers agree that endocrine mechanisms are most likely not involved. Furthermore, there is still uncertainty regarding the optimal amount of creatine required to maximize the ergogenic potential of creatine. An ideal dose may be dependent on individual differences in diet composition, fiber type distribution, sex, age, and initial total muscle creatine concentrations. Creatine requirements may be altered depending on the specific training regimen and exercise configurations. The ability to exercise more intensely with creatine supplementation and thus augment training adaptations has wide application for a large number of athletes who participate in resistance training as a part of their overall training program.

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The biologic effects of nutrients and in product-driven articles commonly seen in popular bodybuilding and fitness magazines. However, it is unclear whether these products can be adequately absorbed by the body. Regardless of nutrient effects, if it is not assimilated into the body, any supposed effect will be negated. This is true especially of chromium and is particularly relevant when discussing chromium’s biologic properties for use in physique augmentation as well as its application in medicine.

Two forms of chromium are found in food, inorganic and organic. They have different absorption rates ranging from 0.4-2% and 10-25%, respectively. Data in humans are sparse, with most of the information on absorption coming from animal studies. 179 In this regard, only organically complexed chromium is active. Inorganic chromium entering the general circulation must be changed into the organic form to be used by the body. Chromium appears to be transported in the body bound to transferrin, albumin, globulins, and lipoproteins. Although data are lacking, the liver is hypothesized to be a major site for the synthesis of organic chromium (active) from the inorganic (inactive) form of the mineral. To date, its precise transport mechanism have yet to be clearly defined. Furthermore, no research studies have established how chromium moves from the digestive tract to sites of synthesis or to various storage depots throughout the body. This void in the literature becomes important when discussing oral dosing.

Three chromium supplements are commercially available: chromium picolinate (organic), chromium nicotinate (organic), and chromium chloride (inorganic). Absorption of these three compounds differ, as do their biologic effects. Chromium chloride is believed to be poorly absorbed and not well used by the body, in supplements available to the public, or in laboratory settings.

Chromium picolinate, the most widely used chromium salt, increases receptor-bound and internalized insulin in cultured cells, whereas nicotinate and chloride salts have different actions on the glucose insulin system. These differences indicate a fertile area of research, and future efforts in the laboratory should look into -

a) Establishing how the different forms of chromium act on insulin tissue responsive

b) Defining the exact mechanism by which chromium is processed and transported within the body.

Another important aspect to consider when discussing chromium usage is the pattern of excretion in athletic populations. Exercise increases chromium loss, but as with other physiological adaptations to stress, the form or type of stress (i.e., the mode of exercise) plays a large role in how the body responds. The effects of stress on urinary chromium loss are correlated directly with cortisol. Most of the data collected to date have been reported on aerobic athletes and have shown an increase in unnary excretion after training. Those interested in the effects of aerobic exercise and chromium loss should read the articles by Anderson et al because this chapter will touch on only those studies associated with resistance training.

Currently, not much research has been done on the effects of weight training and chromium excretion. What has been published indicates that those individuals who are involved in high-intensity resistance training may display altered chromium status owing to increased excretion. Despite this finding it is more than likely that these individuals are easily replacing lost chromium because of the typical high-calorie and nutrient-intake patterns associated with these athletes. Also note that a chromium deficiency is unlikely in strength athletes because the majority of these individuals are ingesting supplements (e.g., meal replacements, protein powders, multivitamins/ minerals, and various thermogenic supplements) that contain 200 µg or more of the mineral.

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To fully understand the use of creatine as an ergogenic aid, one must appreciate its role in energy metabolism. In this regard, a primary objective for students to understand is that skeletal muscle performs mechanical work through the hydrolysis of adenosine triphosphate (ATP). Commonly referred to as the energy currency of a cell,the quantity of ATP present in skeletal muscle is approximately 3 to 5 µmol/kg or 6 mmol/kg of fresh muscle. The continuation of physical work is based on the maintenance of ATP at a rate equal to the rate of its use. Energy reserves consist of intramuscular phosphagen stores (ATP, phosphocreatine [PCr]) and muscle and liver glycogen and adipose stores. The rate and the extent to which these energy sources are used depends on the intensity and/or duration of exercise. To this end, high-intensity anaerobic exercise is supplied almost exclusively by ATP, PCr, and intramuscular glycogen stores.

In a classic series demonstrating the shift of energy usage in skeletal muscle, Hirvonen et al. examined the changes in the intramuscular concentrations of muscle ATP, PCr, and blood lactic acid concentration in sprinters running distances of 40 to 400 meters lasting approximately 4.5 to 50 seconds . Blood lactic acid is a reflection of muscle glycogen usage or glycolysis. Even on casual observation it is interesting to note that despite the increase in running distance, ATP stores initially decline but appear to reach a minimal or critical level after which no further decrease is observed. In contrast, PCr continually and rapidly decreases while the appearance of blood lactic acid or muscle glycogen usage increases. At this point, the reader should embrace two key points. One is to recognize the immediate contribution of all energy systems simultaneously and cooperatively to facilitate energy needs. These energy contributions do not occur sequentially (i.e., one after the other), but instead are time and intensity dependent as to which system dominates. This continued energy production has been conceptualized as a metabolic flux or energy currency that transforms stored energy into muscle contraction.

The maximum work attainable from any energy source can be characterized as both ATP capacity (amount of ATP produced per mole of available substrate) and ATP power (the rate of ATP produced per substrate storage depot). Despite the low intramuscular stores of ATP and PCr within skeletal muscle, their energy production capabilities are exceptional . A review by Sahlin provides an excellent consensus of research findings elaborating on the available energy capacity (mol ATP), maximal ATP power produced from each source (per mmol ATP/kg of dry muscle), as well as the exercise intensity supported and duration of activity allowed per endogenous energy source. It should become readily apparent that events of shorter duration and higher intensity necessitate physical training and nutritional support aimed toward the enhancement of ATP, PCr, and muscle glycogen as opposed to alternative energy sources such as liver glycogen and adipose stores. These sources serve as less adequate sources of ATP power.

Research has shown an improvement in endogenous energy stores of glycogen, PCr, and ATP following 5 months of heavy resistance training although this correlation has not been universally shown. Although changes in resting PCr concentrations might enhance performance during anaerobic activities (e.g., sprinting, weightlifting, etc.), increases in skeletal muscle glycogen may not confer a similar advantage in these types of activities. Strong evidence shows that the dietary manipulation of glycogen stores does not improve various anaerobic performance indices. Also, oral ATP administration does not appear to be prudent owing to the presence of phosphatase enzymes in the blood and gut. These enzymes readily cleave the phosphate portions of ATP. Thus, it appears that oral ATP does not present itself as a suitable ergogenic aid. The same point may be argued for PCr as well. Thus, it is plausible that creatine ingestion may be the best way of augmenting athletic performance vis-a-vis changes in the phosphagen energy system.

One study that examined PCr supplementation showed a performance benefit, albeit to a smaller degree than creatine supplementation. However, any effect of orally ingested PCr would be expected to be mediated by creatine alone because gut phosphatase enzymes would readily cleave off the phosphate portion of the molecule, liberating free creatine in a smaller quantity than when taking the monohydrate form. To date, no human studies have evaluated PCr’s oral absorption and intramuscular uptake. Additionally, blood serum also possesses high phosphatase activity, leading to rapid breakdown of intravenously administered PCr to creatine and phosphate. A study by Peeters et al. determined that PCr-supplemented subjects exhibited a performance response that was approximately 50% less than than that of a creatine monohydrate group. Given that the creatine portion of the monohydrate form makes up about 92% of the molecule and only 50% of the PCr molecule, these results are not surprising. Similarly, although glycolysis is initiated at muscle contraction, increasing glycogen stores may be more advantageous to longer, high-intensity work efforts (>400 m) because of its lower ATP power. These same objectives do not appear to apply to the use of creatine supplementation because both early and more recent studies involving creatine show that it is readily found in food, is absorbed intact, appears rapidly in the blood, and increases intramuscular stores of total creatine and PCr.

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HMB is a metabolite of the branched-chain amino acid leucine and is found naturally in small quantities in catfish, various citrus fruits, and breast milk. Leucine, an essential amino acid, is used for protein synthesis, with the residue being transaminated to alpha-ketoisocaproate (KIC) and then partially oxidized to form HMB. The HMB derived from leucine is converted to beta-hydroxy-beta­methylglutaryl CoA (HMG-CoA) in some tissues and serves as a key carbon source for cholesterol synthesis in various cell types.

This de novo cholesterol synthesis is believed to be behind HMB’s performance-enhancing effects. During periods of cell growth and/or differentiation, HMG-CoA may be a rate-limiting step for cholesterol synthesis, which appears to be a restrictive factor for both cell function and growth. HMB feedings are believed to saturate cells with a source of HMG-CoA, thus providing the tools for cells to undergo a maximal growth response (for strength/power athletes that would be a hypertrophic and/or hyperplastic response with regard to skeletal muscle fibers).

In Vitro Studies

Studies conducted on HMB’s actions at the cellular level have been done in both animal and human cell types. The effect of HMB on skeletal muscle metabolism was investigated by Kostiuk et al. using isolated muscle strips from rats and chicks. Tissues were exposed to different concentrations of HMB and the rates of protein degradation and protein synthesis were measured. This investigation demonstrated HMB inhibited proteolysis by an average of 80% while at the same time increased protein synthesis in both muscle tissues. Cheng et al. also investigated the muscle protein effects of HMB in two cell lines, H9C2 (heart cells) and C2C12 (skeletal muscle cells). Samples were differentiated in culture to myotubes and exposed 2 to 4 days to a to 6 mM HMB. Scientists observed increased beta oxidation of palmitate by 30% decreased lactate dehydrogenase from myotubes by 25% and an increased cellular expression of creatine kinase (CK) by 25%. These results suggest HMB may alter muscle cell metabolism by increasing cellular oxidative capacity and enhancing the expression of muscle-specific proteins-proven by the increased cellular expression of CK.

HMB may also play a part in the immune response to exercise. This effect could apply to preventing overtraining syndrome in strength-power and endurance athletes in whom the immune system is compromised as well as in various medical conditions. In vitro studies investigating the effects of HMB in this regard have demonstrated a positive effect on lymphocytes. Nonnecke and colleagues demonstrated that HMB in high concentrations affected DNA synthesis of bovine lymphocytes in a cell culture medium with adequate in vitro study, HMB was added to chicken-macrophage cultures in various concentrations (range, 100 to 1000 mM). Macrophages are important to immunity because they are involved in producing antibodies and in the mediation of cellular immune responses. In addition, they also participate in the presentation of antigens to lymphocytes. With the addition of HMB, the number of macrophages increased by 20% and nitrite production increased by 29%. In chicks receiving HMB the number of Sephadex-elicited macro phages from peritoneal fluid increased two-to threefold. These data demonstrate HMB exposure induces the generation of macrophages in culture and increases nitrite production and the phagocytic capabilities of macrophages.

Animal Studies

Animal data regarding the beneficial effects of HMB on performance and growth parameters are equivocal and much less intriguing than the human data. Although in vitro data from Kostiuk et al. demonstrated an antiproteolytic and anabolic effect in skeletal muscle, work from Papet et al. showed that high-dose HMB supplementation in lambs had no effect on whole-body protein turnover or skeletal muscle protein synthesis.

Human Studies

Recent human studies suggest HMB displays anticatabolic and anabolic activity in skeletal muscle. Nissen et al. conducted a two-part study to determine whether the administration of HMB to subjects undergoing a weight-training program would elicit any positive effects when compared against those training without supplementation. In part one, untrained subjects randomly received three differing dosages of HMB , and two different protein diets (117 or 175 g/day). The training protocol worked each muscle group once or twice weekly with either free weights or machines. Sessions alternated emphasis between upper and lower body exercises with at least 1 day of rest between workouts. The protocol lasted 3 weeks, with each subject getting 10 total workouts . Each exercise included two warm-up sets with 10 repetitions at 30-60% of the subjects 1-RM. Work sets were performed with three sets of 3 to 5 repetitions at 90% of the 1-RM. The exercises consisted of the following: free­weight bench press, machine latissimus dorsi pull-downs, machine seated row, machine pectoral fly, free-weight preacher biceps curl, and machine triceps push-down; leg press machine, standing calf raise machine, leg flexion machine, leg extension machine, 45­degree inclined situp, inclined leg lift, and back extension. An advanced lifting protocol was used in part two of the study. Twenty eight subjects were supplemented with either 0 or 3.0 g of HMB per day and trained 2 to 3 hours per day 6 days a week for 7 weeks.

In part one of the study, HMB supplementation significantly lowered training-induced muscle proteolysis as measured by urinary 3-methylhistidine excretion during the first 2 weeks of the study. A reduction in plasma creatine kinase was also observed with HMB administration. In subjects receiving HMB, strength increases were greater than those observed in control subjects. When looking at this study critically, a few important issues must be addressed. This was a short-term study and untrained subjects were used. Therefore, although gains in strength were observed, it is impossible to attribute those improvements to the HMB supplement only. Initial improvements in strength in untrained individuals could be a result of increased voluntary activation of muscle (neural adaptation), rather than the accretion of protein. Staron et al showed that approximately resistance training sessions are required to induce increases in lean body mass or muscle mass. Thus, using untrained subjects during a short-term trial severely limits drawing any conclusions to the benefit of HMB in terms of increasing muscle mass and strength.

In the second study, fat-free mass increased in the HMB­supplemented group at various intervals throughout the study, but not at the conclusion of the study. After the seventh week, strength improved in the bench press, but not the squat or hang clean exercises in the HMB-supplemented group. Thus, over time it is apparent that the effects of HMB may actually diminish. In this phase of the investigation, trained subjects were used, but the control group was stronger at the onset of the study. Therefore, these subjects did not attain the same percentage gains as the two groups receiving HMB.

Although the majority of research is conducted in male subjects, using female subjects is important as well. This research proves valuable from a scientific standpoint because of the differing hormonal milieu in women as well as from a health standpoint (i.e. weight control, prevention of osteoporosis, as well as possible safety concerns for pregnant females). With the increasing involvement of women in strength training and their interest in altering body composition, science should address the female organism’s response to nutritional ergogenic aids. To determine if the same antiproteolytic effects occur in women as in their male counterparts undergoing vigorous strength training, scientists from Iowa State University, in Ames, Iowa investigated the effects of HMB (3 g/day) on 36 nonexercising females, and a second study investigated HMB supplementation (3 g/day) or a placebo given to 37 women undergoing a 3 day-per-week resistance training program. Body composition was measured via total body electrical conductivity (TOBEC) in the first part of the study and underwater weighing in the second. In contrast to the study conducted by Nissen et al, these researchers determined that HMB supplementation, combined with weight training, increased gains in lean body mass and strength. Untrained sedentary subjects receiving HMB showed no changes in lean or fat mass.

Vukovich et al. studied the effect of calcium HMB on maximal oxygen consumption and maximal blood lactate concentration in endurance-trained cyclists. During this trial, eight cyclists randomly completed three separate supplementation periods. Each supplement was administered for 2 weeks followed by a 2-week washout period. Supplements administered to the subjects were HMB (3 g/day), leucine (3 g/day), and a placebo (3 g/day). Before and after each supplementation period, subjects completed a VO2peak test with blood samples obtained immediately following exercise to determine the maximal appearance of blood lactic acid. After 2 weeks of HMB supplementation, a significant increase in VO2peak was noted for the calcium HMB group. VO2peak was unaffected by leucine and placebo supplementation. The HMB group also showed a significantly greater time to reach VO2peak, whereas leucine and placebo elicited no effect on this variable. Maximal blood lactic acid concentrations were unaffected by supplementation but tended to be higher following HMB supplementation. Thus, the authors concluded that HMB supplementation could have positive effects on performance by increasing V02peak Although these results may not appear to be of importance to the strength athlete per se, it may be beneficial to those athletes participating in running events between 400 and 1600 meters.

Whereas HMB alone appears to have limited effects in an otherwise healthy population, some researchers have examined the effects of ingesting a calcium HMB/glucose supplement combined with or without creatine during sprint and strength-training exercises. In a double-blind and randomized manner, 41 NCAA Division IA football players were match-paired and assigned to supplement their diets for 28 days with either -

1) A placebo containing 99 g/day of glucose, 3 g/day of taurine, 1.1 g/day of disodium phosphate, and 1.2 g/day of potassium phosphate

2) The PotPh mixture with 3 g/day of calcium HMB

3) the PotPh/HMB mixture with 15.75 g/day of HPCD pure creatine monohydrate.

In this study, subjects participated in a resistance-training program and an agility/sprint training program . On days 0 and 28, subjects performed 126-second sprints on a computerized cycle ergometer with 30-second rest periods between sprints. Subjects also performed maximal repetition tests at 70% of estimated 1-RM on the isotonic bench press, upright squat, and power clean. Using ANCOVA and ANOVA statistical techniques, this group showed that work output tended to be greater in the HMB and HMB/creatine trials. Mean change in work tended to also be greater in the HMB and HMB/creatine groups. Gains in lifting volume tended to be greater in the HMB/creatine group for the bench press squat , and clean. Results revealed that adding creatine to HMB could enhance strength and/or anaerobic capacity. However, additional research is necessary because this investigation did not control for creatine effects by using a creatine-only group.

Because of the possible effects of HMB in decreasing proteolysis and increasing protein synthesis in skeletal muscle, this compound may be effective in the medical treatment of certain conditions such as certain muscle wasting diseases or in postsurgical recovery. Both practitioners and patients find it particularly interesting that HMB may have beneficial effects in preventing the profound decrease in muscle tissue and immune system function observed in the late stages of AIDS. In certain conditions L-arginine and L-glutamine have been shown to increase immune function in humans and to have beneficial effects on skeletal muscle. In an interesting study presented at the XII World AIDS Conference in June of 1998, Clark et al. investigated the possibility that an amino acid combination administered with HMB could result in a synergistic action positively affecting muscle metabolism and immune function. Subjects were recruited from HIV clinics to participate in a randomized, double-blind, placebo-controlled 8-week study in which they received an amino acid mixture containing 14 g arginine, 14 g glutamine, and 3 g HMB daily. Lean body mass and fat mass were measured by an air displacement plethysmography at 0, 4, and 8 weeks. The abstract presented data from 16 subjects and results showed subjects who consumed the amino acid/HMB mixture gained 3.00 ± 0.50 kg , whereas the placebo group gained 0.37 ± 0.84 kg.Weight gain with the experimental group was predominately lean tissue and fat 0.60 ± 1.70 kg). The placebo group did not gain any lean tissue, but did accrue fat . Measures of immune system integrity demonstrated that the amino acid/HMB mixture increased absolute CD4 numbers by 17.3 ± 28.2 cells/mm versus 49.0 ± 27.4 and absolute lymphocytes by 0.29 ± 0.14 1000/mm versus -0.31 ± 0.15. Although it appears that HMB might provide a useful tool to those treating HIV-associated wasting syndrome, it would have been informative to have one group of subjects ingesting L-arginine and L-glutamine alone and in combination with creatine. As was previously demonstrated at the XI International Conference on AIDS, Daniel et al. showed that a formula containing creatine was effective in increasing total body mass in HIV-positive patients and, therefore, this presents an interesting avenue of future investigation for individuals afflicted with this disease.

Safety and Toxicity

According to existing human data, HMB appears to be safe and well tolerated. Studies ranging in length from 1 to 8 weeks have shown that up to 3 g/day of HMB is safe in male and female subjects, this is supported by the lack of adverse physical effects determined by blood chemistry analysis.

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PCr’s major cellular function is to maintain metabolic flux during the early onset of exercise and high-intensity work performance. Given the observed greater ATP production associated with PCr, and coupled with the increase in PCr associated with creatine supplementation, the potential for an increase in anaerobic work output is fully justifiable. Moreover, the maintenance of PCr concentrations appears to correlate well with the development of fatigue in that its decrease is associated with a decline in muscular force. Infante et al. showed a direct relationship between external work and PCr breakdown in the frog rectus abdominis muscle. Spande and Schottelius also showed a direct relationship between force production and PCr stores in isolated mouse soleus muscle that was tetanically stimulated. In this model, they observed a decline in PCr that was directly proportional to the development and maintenance of isometric tetanic force.

In humans, Hirvonen et al. concluded that the slowing of running speed during maximal work efforts is related to a decline in the energy production brought forth from ATP and PCr. This effect may be a result of muscle fiber type differences in the endogenous stores of each substrate. This premise is supported by the observations of others who have noted that type II muscle fibers possess higher initial levels of PCr and, consequently, greater rates of PCr usage than do type I muscle fibers during high-intensity exercise. PCr and glycogen recovery also appears to be slower in type II fibers following high-intensity exercise. Moreover, PCr resynthesis during recovery has been shown to be an oxygen-dependent process that exhibits a two-component or biphasic pattern. The first (fast component) has a half-time of approximately 22 seconds, whereas the second (slow component) is longer than 170 seconds. During continuous or intermittent high-intensity exercise, the resynthesis rate of PCr plays an important role in the force capabilities that active muscle can generate owing to the heavy reliance on PCr and ATP.

When PCr levels are not given adequate recovery time, performance is impaired and power output is decreased Conversely, when recovery is prolonged, increased PCr concentration is correlated with greater power output during consecutivecycle ergometer sprints when rest periods of either 90 or 180 seconds are allowed. Thus, the possibility of creatine supplementation increasing PCr recovery is important because it is the recovery of PCr following high-intensity exercise that allows athletes to continue high-intensity activity more effectively. If it is possible to increase the rate of resynthesis and PCr storage capacity through supplementation, then the use of creatine has a valid physiological base from which to assess utility

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